Several approaches have been taken in the past to remove contaminants from waste gas streams, which may arise from various sources, where the contaminants may be in vaporous of particulate form of liquid or solid nature. A well known standard approach for removing contaminants from a waste gas stream is to pass countercurrently through the gas stream a scrubbing solution. Such scrubbing solution may be sprayed downwardly in a scrubbing tower where the gases move upwardly through the tower. The tower may be of the packed type having various forms of packing well known in the art to enhance the gas liquid contact for removing vaporous contaminants. Other approaches for removing particulate contaminants involve spraying either cocurrently or countercurrently to the air flow, a spray which wets the particles and causes them to fall out under the influence of gravity or the wetted particles may be separated from the gas stream by using various types of centrifugal treatments.
Canadian Pat. No. 352,850 and U.S. Pat. Nos. 2,195,707, 2,763,982, 3,651,622, 3,653,187 and 4,067,703 disclose various approaches to introducing a scrubbing spray into the gas stream and then separating the wetted particulate contaminants from the gas stream by passing the treated gas stream through various types of centrifugal separation devices which may be in the form of centrifugal fans.
Alternate approaches involve the introduction of a spray into the gas stream for purposes of wetting the particles with the spray and removing the particles by collecting them on the walls of the apparatus, or by filtration. Such devices are disclosed in U.S. Pat. Nos. 2,858,903, 2,935,375 and 3,016,979. There is, however, no consideration given in this last approach to using any form of device which would cause a vigorous mixing of the fine spray of scrubbing solution into the gas stream to enhance the wetting of the particulate contaminants. In addition, one of these approaches, as disclosed in U.S. Pat. No. 2,935,375, requires high energy input in the use of a venturi which necessitates considerable horsepower to drive the air compressor to accomplish removal. For example, a 200 horsepower motor may be necessary so that the velocity of the stream of gas, as it passes through the venturi, would be increased from 3,000 feet per minute to about 18,000 feet per minute at the point of constriction in the venturi in order to achieve the desired atomization of the introduced spray in the gas stream.
Further difficulty encountered with the prior art approaches is that none of them have produced an economical energy efficient approach to removing very minute particulate contaminants which may be as small as one micron in size.
It is, therefore, an object of this invention to provide an efficient removal of small minute particulate liquid and/or solid contaminants from a waste gas stream. Such object may be applied to the removal of contaminants from a waste gas stream which is generated in a drying oven for freshly printed materials.